This invention relates to the field of surgical instruments, particularly instruments which come into contact with other instruments or other portions of an instrument during use or storage, such as instruments having teeth, serrations, a cutting edge, or being otherwise susceptible to wear. Most particularly, the invention relates to a method for making high toughness surgical scissors and a method for imparting such toughness to them.
Surgical cutting instruments, in particular scissors, must give a sharp clean cut in order to prevent unexpected and unwanted damage to delicate tissues. When surgical instruments are being handled in groups, particularly during a sterilization process, they frequently come in contact with one another which can tend to dull a cutting edge. In addition, when scissors are in use, each cut generally tends to dull the cutting edge as it contacts the adjacent blade. Thus it is highly desirable to provide a toughened wearing surface on a surgical instrument to prevent the frequent necessity for sharpening the instrument. In addition, each sharpening removes a small amount of metal until the instrument must eventually be discarded.
Presently available surgical scissors have an average useful life of about three years, because of the limited life of the cutting edge. Heretofore, attempts to increase this limited useful life have included using high quality stainless steels and tungsten carbide inserts on cutting surfaces, particularly on surgical scissors. The present invention provides a surgical instrument have a tough wearing surface with a useful life of at least double that of presently available instruments. In addition, sharpening of such instruments is sharply curtailed with attendant cost savings, and reduced repairs.
Titanium nitride is both inert and has a high degree of lubricity, which makes titanium nitride coated stainless steel the ideal material for surgical instruments, as they give the surgeon excellent control of the instrument during surgery by reducing resistance during cutting, and promoting release of tissue, as well as avoiding contamination or infection from foreign substances.
Instruments with members that are connected by box locks generally accumulate blood in the region of the box locks during use. Such blood becomes caked and tightly adherent. The instruments are usually cleaned by ultrasound, but this does not always break loose the dried and nearly crystallized blood. In addition, over a period of time cleaning by ultrasound promotes the formation of cracks within these box locks. Instruments utilizing box locks are generally discarded either because of blood caking in multiple layers or crack formation which also retains blood. By coating all parts of a box lock with titanium nitride before assembly, the lubricity of the titanium nitride resists adherance of dried blood, as well as cooperating with the ultrasound cleaning treatment to promote removal of dried blood from the instrument.